

/*
* regcomp and regexec -- regsub and regerror are elsewhere
*
*      Copyright (c) 1986 by University of Toronto.
*      Written by Henry Spencer.  Not derived from licensed software.
*
*      Permission is granted to anyone to use this software for any
*      purpose on any computer system, and to redistribute it freely,
*      subject to the following restrictions:
*
*      1. The author is not responsible for the consequences of use of
*              this software, no matter how awful, even if they arise
*              from defects in it.
*
*      2. The origin of this software must not be misrepresented, either
*              by explicit claim or by omission.
*
*      3. Altered versions must be plainly marked as such, and must not
*              be misrepresented as being the original software.
*
* Beware that some of this code is subtly aware of the way operator
* precedence is structured in regular expressions.  Serious changes in
* regular-expression syntax might require a total rethink.
*/
/*
#include <stdio.h>
#include <string.h>*/
#include "regexp.h"
#include "regmagic.h"
#include "cg_local.h"

void regerror( char *string )
{
    CG_Printf(string);
}
/*
* The "internal use only" fields in regexp.h are present to pass info from
* compile to execute that permits the execute phase to run lots faster on
* simple cases.  They are:
*
* regstart     char that must begin a match; '\0' if none obvious
* reganch      is the match anchored (at beginning-of-line only)?
* regmust      string (pointer into program) that match must include, or NULL
* regmlen      length of regmust string
*
* Regstart and reganch permit very fast decisions on suitable starting points
* for a match, cutting down the work a lot.  Regmust permits fast rejection
* of lines that cannot possibly match.  The regmust tests are costly enough
* that regcomp() supplies a regmust only if the r.e. contains something
* potentially expensive (at present, the only such thing detected is * or +
* at the start of the r.e., which can involve a lot of backup).  Regmlen is
* supplied because the test in regexec() needs it and regcomp() is computing
* it anyway.
*/

/*
* Structure for regexp "program".  This is essentially a linear encoding
* of a nondeterministic finite-state machine (aka syntax charts or
* "railroad normal form" in parsing technology).  Each node is an opcode
* plus a "next" pointer, possibly plus an operand.  "Next" pointers of
* all nodes except BRANCH implement concatenation; a "next" pointer with
* a BRANCH on both ends of it is connecting two alternatives.  (Here we
* have one of the subtle syntax dependencies:  an individual BRANCH (as
* opposed to a collection of them) is never concatenated with anything
* because of operator precedence.)  The operand of some types of node is
* a literal string; for others, it is a node leading into a sub-FSM.  In
* particular, the operand of a BRANCH node is the first node of the branch.
* (NB this is *not* a tree structure:  the tail of the branch connects
* to the thing following the set of BRANCHes.)  The opcodes are:
*/

/* definition   number        opnd?        meaning */
#define END        0        /* no        End of program. */
#define BOL        1        /* no        Match "" at beginning of line. */
#define EOL        2        /* no        Match "" at end of line. */
#define ANY        3        /* no        Match any one character. */
#define ANYOF        4        /* str        Match any character in this string. */
#define ANYBUT        5        /* str        Match any character not in this string. */
#define BRANCH        6        /* node        Match this alternative, or the next... */
#define BACK        7        /* no        Match "", "next" ptr points backward. */
#define EXACTLY        8        /* str        Match this string. */
#define NOTHING        9        /* no        Match empty string. */
#define STAR        10        /* node        Match this (simple) thing 0 or more times. */
#define PLUS        11        /* node        Match this (simple) thing 1 or more times. */
#define OPEN        20        /* no        Mark this point in input as start of #n. */
/*        OPEN+1 is number 1, etc. */
#define CLOSE        30        /* no        Analogous to OPEN. */

/*
* Opcode notes:
*
* BRANCH       The set of branches constituting a single choice are hooked
*              together with their "next" pointers, since precedence prevents
*              anything being concatenated to any individual branch.  The
*              "next" pointer of the last BRANCH in a choice points to the
*              thing following the whole choice.  This is also where the
*              final "next" pointer of each individual branch points; each
*              branch starts with the operand node of a BRANCH node.
*
* BACK         Normal "next" pointers all implicitly point forward; BACK
*              exists to make loop structures possible.
*
* STAR,PLUS    '?', and complex '*' and '+', are implemented as circular
*              BRANCH structures using BACK.  Simple cases (one character
*              per match) are implemented with STAR and PLUS for speed
*              and to minimize recursive plunges.
*
* OPEN,CLOSE   ...are numbered at compile time.
*/

/*
* A node is one char of opcode followed by two chars of "next" pointer.
* "Next" pointers are stored as two 8-bit pieces, high order first.  The
* value is a positive offset from the opcode of the node containing it.
* An operand, if any, simply follows the node.  (Note that much of the
* code generation knows about this implicit relationship.)
*
* Using two bytes for the "next" pointer is vast overkill for most things,
* but allows patterns to get big without disasters.
*/
#define OP(p)        (*(p))
#define NEXT(p)        (((*((p)+1)&0377)<<8) + (*((p)+2)&0377))
#define OPERAND(p)        ((p) + 3)

/*
* See regmagic.h for one further detail of program structure.
*/


/*
* Utility definitions.
*/
#ifndef CHARBITS
#define UCHARAT(p)        ((int)*(unsigned char *)(p))
#else
#define UCHARAT(p)        ((int)*(p)&CHARBITS)
#endif

#define FAIL(m)        { regerror(m); return(NULL); }
#define ISMULT(c)        ((c) == '*' || (c) == '+' || (c) == '?')
#define META        "^$.[()|?+*\\"

/*
* Flags to be passed up and down.
*/
#define HASWIDTH        01        /* Known never to match null string. */
#define SIMPLE                02        /* Simple enough to be STAR/PLUS operand. */
#define SPSTART                04        /* Starts with * or +. */
#define WORST                0        /* Worst case. */

/*
* Global work variables for regcomp().
*/
static char *regparse;          /* Input-scan pointer. */
static int regnpar;		/* () count. */
static char regdummy;
static char *regcode;           /* Code-emit pointer; &regdummy = don't. */
static long regsize;		/* Code size. */

/*
* Forward declarations for regcomp()'s friends.
*/
#ifndef STATIC
#define STATIC        static
#endif
STATIC char *reg();
STATIC char *regbranch();
STATIC char *regpiece();
STATIC char *regatom();
STATIC char *regnode();
STATIC char *regnext();
STATIC void regc();
STATIC void reginsert();
STATIC void regtail();
STATIC void regoptail();
#ifdef STRCSPN
STATIC int strcspn();
#endif

/*
- regcomp - compile a regular expression into internal code
*
* We can't allocate space until we know how big the compiled form will be,
* but we can't compile it (and thus know how big it is) until we've got a
* place to put the code.  So we cheat:  we compile it twice, once with code
* generation turned off and size counting turned on, and once "for real".
* This also means that we don't allocate space until we are sure that the
* thing really will compile successfully, and we never have to move the
* code and thus invalidate pointers into it.  (Note that it has to be in
* one piece because free() must be able to free it all.)
*
* Beware that the optimization-preparation code in here knows about some
* of the structure of the compiled regexp.
*/
regexp *
regcomp(exp)
char *exp;
{
    register regexp *r;
    register char *scan;
    register char *longest;
    register int len;
    int flags;
    //     extern char *malloc();

    // reinit memory
    CG_InitMemory();

    if (exp == NULL)
        FAIL("NULL argument");

    /* First pass: determine size, legality. */
    regparse = exp;
    regnpar = 1;
    regsize = 0L;
    regcode = &regdummy;
    regc(MAGIC);
    if (reg(0, &flags) == NULL)
        return(NULL);

    /* Small enough for pointer-storage convention? */
    if (regsize >= 32767L)                /* Probably could be 65535L. */
        FAIL("regexp too big");

    /* Allocate space. */
    r = (regexp *)CG_Alloc(sizeof(regexp) + (unsigned)regsize);
    if (r == NULL)
        FAIL("out of space");

    /* Second pass: emit code. */
    regparse = exp;
    regnpar = 1;
    regcode = r->program;
    regc(MAGIC);
    if (reg(0, &flags) == NULL)
        return(NULL);

    /* Dig out information for optimizations. */
    r->regstart = '\0';        /* Worst-case defaults. */
    r->reganch = 0;
    r->regmust = NULL;
    r->regmlen = 0;
    scan = r->program+1;                        /* First BRANCH. */
    if (OP(regnext(scan)) == END) {		 /* Only one top-level choice. */
        scan = OPERAND(scan);

        /* Starting-point info. */
        if (OP(scan) == EXACTLY)
            r->regstart = *OPERAND(scan);
        else if (OP(scan) == BOL)
            r->reganch++;

        /*
        * If there's something expensive in the r.e., find the
        * longest literal string that must appear and make it the
        * regmust.  Resolve ties in favor of later strings, since
        * the regstart check works with the beginning of the r.e.
        * and avoiding duplication strengthens checking.  Not a
        * strong reason, but sufficient in the absence of others.
        */
        if (flags&SPSTART) {
            longest = NULL;
            len = 0;
            for (; scan != NULL; scan = regnext(scan))
                if (OP(scan) == EXACTLY && strlen(OPERAND(scan)) >= len) {
                    longest = OPERAND(scan);
                    len = strlen(OPERAND(scan));
                }
            r->regmust = longest;
            r->regmlen = len;
        }
    }

    return(r);
}

/*
- reg - regular expression, i.e. main body or parenthesized thing
*
* Caller must absorb opening parenthesis.
*
* Combining parenthesis handling with the base level of regular expression
* is a trifle forced, but the need to tie the tails of the branches to what
* follows makes it hard to avoid.
*/
static char *
reg(paren, flagp)
int paren;                      /* Parenthesized? */
int *flagp;
{
    register char *ret;
    register char *br;
    register char *ender;
    register int parno;
    int flags;

    *flagp = HASWIDTH;        /* Tentatively. */

    /* Make an OPEN node, if parenthesized. */
    if (paren) {
        if (regnpar >= NSUBEXP)
            FAIL("too many ()");
        parno = regnpar;
        regnpar++;
        ret = regnode(OPEN+parno);
    } else
        ret = NULL;

    /* Pick up the branches, linking them together. */
    br = regbranch(&flags);
    if (br == NULL)
        return(NULL);
    if (ret != NULL)
        regtail(ret, br);        /* OPEN -> first. */
    else
        ret = br;
    if (!(flags&HASWIDTH))
        *flagp &= ~HASWIDTH;
    *flagp |= flags&SPSTART;
    while (*regparse == '|') {
        regparse++;
        br = regbranch(&flags);
        if (br == NULL)
            return(NULL);
        regtail(ret, br);        /* BRANCH -> BRANCH. */
        if (!(flags&HASWIDTH))
            *flagp &= ~HASWIDTH;
        *flagp |= flags&SPSTART;
    }

    /* Make a closing node, and hook it on the end. */
    ender = regnode((paren) ? CLOSE+parno : END);
    regtail(ret, ender);

    /* Hook the tails of the branches to the closing node. */
    for (br = ret; br != NULL; br = regnext(br))
        regoptail(br, ender);

    /* Check for proper termination. */
    if (paren && *regparse++ != ')') {
        FAIL("unmatched ()");
    } else if (!paren && *regparse != '\0') {
        if (*regparse == ')') {
            FAIL("unmatched ()");
        } else
            FAIL("junk on end");        /* "Can't happen". */
        /* NOTREACHED */
    }

    return(ret);
}

/*
- regbranch - one alternative of an | operator
*
* Implements the concatenation operator.
*/
static char *
regbranch(flagp)
int *flagp;
{
    register char *ret;
    register char *chain;
    register char *latest;
    int flags;

    *flagp = WORST;                /* Tentatively. */

    ret = regnode(BRANCH);
    chain = NULL;
    while (*regparse != '\0' && *regparse != '|' && *regparse != ')') {
        latest = regpiece(&flags);
        if (latest == NULL)
            return(NULL);
        *flagp |= flags&HASWIDTH;
        if (chain == NULL)        /* First piece. */
            *flagp |= flags&SPSTART;
        else
            regtail(chain, latest);
        chain = latest;
    }
    if (chain == NULL)        /* Loop ran zero times. */
        (void) regnode(NOTHING);

    return(ret);
}

/*
- regpiece - something followed by possible [*+?]
*
* Note that the branching code sequences used for ? and the general cases
* of * and + are somewhat optimized:  they use the same NOTHING node as
* both the endmarker for their branch list and the body of the last branch.
* It might seem that this node could be dispensed with entirely, but the
* endmarker role is not redundant.
*/
static char *
regpiece(flagp)
int *flagp;
{
    register char *ret;
    register char op;
    register char *next;
    int flags;

    ret = regatom(&flags);
    if (ret == NULL)
        return(NULL);

    op = *regparse;
    if (!ISMULT(op)) {
        *flagp = flags;
        return(ret);
    }

    if (!(flags&HASWIDTH) && op != '?')
        FAIL("*+ operand could be empty");
    *flagp = (op != '+') ? (WORST|SPSTART) : (WORST|HASWIDTH);

    if (op == '*' && (flags&SIMPLE))
        reginsert(STAR, ret);
    else if (op == '*') {
        /* Emit x* as (x&|), where & means "self". */
        reginsert(BRANCH, ret);                        /* Either x */
        regoptail(ret, regnode(BACK));		 /* and loop */
        regoptail(ret, ret);				 /* back */
        regtail(ret, regnode(BRANCH));		 /* or */
        regtail(ret, regnode(NOTHING));		 /* null. */
    } else if (op == '+' && (flags&SIMPLE))
        reginsert(PLUS, ret);
    else if (op == '+') {
        /* Emit x+ as x(&|), where & means "self". */
        next = regnode(BRANCH);                        /* Either */
        regtail(ret, next);
        regtail(regnode(BACK), ret);                /* loop back */
        regtail(next, regnode(BRANCH));	      /* or */
        regtail(ret, regnode(NOTHING));	      /* null. */
    } else if (op == '?') {
        /* Emit x? as (x|) */
        reginsert(BRANCH, ret);                        /* Either x */
        regtail(ret, regnode(BRANCH));		 /* or */
        next = regnode(NOTHING);			 /* null. */
        regtail(ret, next);
        regoptail(ret, next);
    }
    regparse++;
    if (ISMULT(*regparse))
        FAIL("nested *?+");

    return(ret);
}

/*
- regatom - the lowest level
*
* Optimization:  gobbles an entire sequence of ordinary characters so that
* it can turn them into a single node, which is smaller to store and
* faster to run.  Backslashed characters are exceptions, each becoming a
* separate node; the code is simpler that way and it's not worth fixing.
*/
static char *
regatom(flagp)
int *flagp;
{
    register char *ret;
    int flags;

    *flagp = WORST;                /* Tentatively. */

    switch (*regparse++) {
    case '^':
        ret = regnode(BOL);
        break;
    case '$':
        ret = regnode(EOL);
        break;
    case '.':
        ret = regnode(ANY);
        *flagp |= HASWIDTH|SIMPLE;
        break;
    case '[': {
            register int class;
            register int classend;

            if (*regparse == '^') {        /* Complement of range. */
                ret = regnode(ANYBUT);
                regparse++;
            } else
                ret = regnode(ANYOF);
            if (*regparse == ']' || *regparse == '-')
                regc(*regparse++);
            while (*regparse != '\0' && *regparse != ']') {
                if (*regparse == '-') {
                    regparse++;
                    if (*regparse == ']' || *regparse == '\0')
                        regc('-');
                    else {
                        class = UCHARAT(regparse-2)+1;
                        classend = UCHARAT(regparse);
                        if (class > classend+1)
                            FAIL("invalid [] range");
                        for (; class <= classend; class++)
                            regc(class);
                        regparse++;
                    }
                } else
                    regc(*regparse++);
            }
            regc('\0');
            if (*regparse != ']')
                FAIL("unmatched []");
            regparse++;
            *flagp |= HASWIDTH|SIMPLE;
        }
        break;
    case '(':
        ret = reg(1, &flags);
        if (ret == NULL)
            return(NULL);
        *flagp |= flags&(HASWIDTH|SPSTART);
        break;
    case '\0':
    case '|':
    case ')':
        FAIL("internal urp");        /* Supposed to be caught earlier. */
        break;
    case '?':
    case '+':
    case '*':
        FAIL("?+* follows nothing");
        break;
    case '\\':
        if (*regparse == '\0')
            FAIL("trailing \\");
        ret = regnode(EXACTLY);
        regc(*regparse++);
        regc('\0');
        *flagp |= HASWIDTH|SIMPLE;
        break;
    default: {
            register int len;
            register char ender;

            regparse--;
            len = strcspn(regparse, META);
            if (len <= 0)
                FAIL("internal disaster");
            ender = *(regparse+len);
            if (len > 1 && ISMULT(ender))
                len--;                /* Back off clear of ?+* operand. */
            *flagp |= HASWIDTH;
            if (len == 1)
                *flagp |= SIMPLE;
            ret = regnode(EXACTLY);
            while (len > 0) {
                regc(*regparse++);
                len--;
            }
            regc('\0');
        }
        break;
    }

    return(ret);
}

/*
- regnode - emit a node
*/
static char *                   /* Location. */
regnode(op)
char op;
{
    register char *ret;
    register char *ptr;

    ret = regcode;
    if (ret == &regdummy) {
        regsize += 3;
        return(ret);
    }

    ptr = ret;
    *ptr++ = op;
    *ptr++ = '\0';                /* Null "next" pointer. */
    *ptr++ = '\0';
    regcode = ptr;

    return(ret);
}

/*
- regc - emit (if appropriate) a byte of code
*/
static void
regc(b)
char b;
{
    if (regcode != &regdummy)
        *regcode++ = b;
    else
        regsize++;
}

/*
- reginsert - insert an operator in front of already-emitted operand
*
* Means relocating the operand.
*/
static void
reginsert(op, opnd)
char op;
char *opnd;
{
    register char *src;
    register char *dst;
    register char *place;

    if (regcode == &regdummy) {
        regsize += 3;
        return;
    }

    src = regcode;
    regcode += 3;
    dst = regcode;
    while (src > opnd)
        *--dst = *--src;

    place = opnd;                /* Op node, where operand used to be. */
    *place++ = op;
    *place++ = '\0';
    *place++ = '\0';
}

/*
- regtail - set the next-pointer at the end of a node chain
*/
static void
regtail(p, val)
char *p;
char *val;
{
    register char *scan;
    register char *temp;
    register int offset;

    if (p == &regdummy)
        return;

    /* Find last node. */
    scan = p;
    for (;;) {
        temp = regnext(scan);
        if (temp == NULL)
            break;
        scan = temp;
    }

    if (OP(scan) == BACK)
        offset = scan - val;
    else
        offset = val - scan;
    *(scan+1) = (offset>>8)&0377;
    *(scan+2) = offset&0377;
}

/*
- regoptail - regtail on operand of first argument; nop if operandless
*/
static void
regoptail(p, val)
char *p;
char *val;
{
    /* "Operandless" and "op != BRANCH" are synonymous in practice. */
    if (p == NULL || p == &regdummy || OP(p) != BRANCH)
        return;
    regtail(OPERAND(p), val);
}

/*
* regexec and friends
*/

/*
* Global work variables for regexec().
*/
static char *reginput;          /* String-input pointer. */
static char *regbol;		/* Beginning of input, for ^ check. */
static char **regstartp;	/* Pointer to startp array. */
static char **regendp;		/* Ditto for endp. */

/*
* Forwards.
*/
STATIC int regtry();
STATIC int regmatch();
STATIC int regrepeat();

#ifdef DEBUG
int regnarrate = 0;
void regdump();
STATIC char *regprop();
#endif

/*
- regexec - match a regexp against a string
*/
int
regexec(prog, string)
register regexp *prog;
register char *string;
{
    register char *s;
    extern char *strchr();

    /* Be paranoid... */
    if (prog == NULL || string == NULL) {
        regerror("NULL parameter");
        return(0);
    }

    /* Check validity of program. */
    if (UCHARAT(prog->program) != MAGIC) {
        regerror("corrupted program");
        return(0);
    }


    /* If there is a "must appear" string, look for it. */
    if (prog->regmust != NULL) {
        s = string;
        while ((s = strchr(s, prog->regmust[0])) != NULL) {
            if (Q_strncmp(s, prog->regmust, prog->regmlen) == 0)
                break;        /* Found it. */
            s++;
        }
        if (s == NULL)        /* Not present. */
            return(0);
    }

    /* Mark beginning of line for ^ . */
    regbol = string;

    /* Simplest case:  anchored match need be tried only once. */
    if (prog->reganch)
        return(regtry(prog, string));

    /* Messy cases:  unanchored match. */
    s = string;
    if (prog->regstart != '\0')
        /* We know what char it must start with. */
        while ((s = strchr(s, prog->regstart)) != NULL) {
            if (regtry(prog, s))
                return(1);
            s++;
        }
    else
        /* We don't -- general case. */
        do {
            if (regtry(prog, s))
                return(1);
        } while (*s++ != '\0');

    /* Failure. */
    return(0);
}

/*
- regtry - try match at specific point
*/
static int                      /* 0 failure, 1 success */
regtry(prog, string)
regexp *prog;
char *string;
{
    register int i;
    register char **sp;
    register char **ep;

    reginput = string;
    regstartp = prog->startp;
    regendp = prog->endp;

    sp = prog->startp;
    ep = prog->endp;
    for (i = NSUBEXP; i > 0; i--) {
        *sp++ = NULL;
        *ep++ = NULL;
    }
    if (regmatch(prog->program + 1)) {
        prog->startp[0] = string;
        prog->endp[0] = reginput;
        return(1);
    } else
        return(0);
}

/*
- regmatch - main matching routine
*
* Conceptually the strategy is simple:  check to see whether the current
* node matches, call self recursively to see whether the rest matches,
* and then act accordingly.  In practice we make some effort to avoid
* recursion, in particular by going through "ordinary" nodes (that don't
* need to know whether the rest of the match failed) by a loop instead of
* by recursion.
*/
static int                      /* 0 failure, 1 success */
regmatch(prog)
char *prog;
{
    register char *scan;        /* Current node. */
    char *next;		 /* Next node. */
    extern char *strchr();

    scan = prog;
#ifdef DEBUG
    if (scan != NULL && regnarrate)
        fprintf(stderr, "%s(\n", regprop(scan));
#endif
    while (scan != NULL) {
#ifdef DEBUG
        if (regnarrate)
            fprintf(stderr, "%s...\n", regprop(scan));
#endif
        next = regnext(scan);

        switch (OP(scan)) {
        case BOL:
            if (reginput != regbol)
                return(0);
            break;
        case EOL:
            if (*reginput != '\0')
                return(0);
            break;
        case ANY:
            if (*reginput == '\0')
                return(0);
            reginput++;
            break;
        case EXACTLY: {
                register int len;
                register char *opnd;

                opnd = OPERAND(scan);
                /* Inline the first character, for speed. */
                if (*opnd != *reginput)
                    return(0);
                len = strlen(opnd);
                if (len > 1 && Q_strncmp(opnd, reginput, len) != 0)
                    return(0);
                reginput += len;
            }
            break;
        case ANYOF:
            if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) == NULL)
                return(0);
            reginput++;
            break;
        case ANYBUT:
            if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) != NULL)
                return(0);
            reginput++;
            break;
        case NOTHING:
            break;
        case BACK:
            break;
        case OPEN+1:
        case OPEN+2:
        case OPEN+3:
        case OPEN+4:
        case OPEN+5:
        case OPEN+6:
        case OPEN+7:
        case OPEN+8:
        case OPEN+9: {
                register int no;
                register char *save;

                no = OP(scan) - OPEN;
                save = reginput;

                if (regmatch(next)) {
                    /*
                    * Don't set startp if some later
                    * invocation of the same parentheses
                    * already has.
                    */
                    if (regstartp[no] == NULL)
                        regstartp[no] = save;
                    return(1);
                } else
                    return(0);
            }
            break;
        case CLOSE+1:
        case CLOSE+2:
        case CLOSE+3:
        case CLOSE+4:
        case CLOSE+5:
        case CLOSE+6:
        case CLOSE+7:
        case CLOSE+8:
        case CLOSE+9: {
                register int no;
                register char *save;

                no = OP(scan) - CLOSE;
                save = reginput;

                if (regmatch(next)) {
                    /*
                    * Don't set endp if some later
                    * invocation of the same parentheses
                    * already has.
                    */
                    if (regendp[no] == NULL)
                        regendp[no] = save;
                    return(1);
                } else
                    return(0);
            }
            break;
        case BRANCH: {
                register char *save;

                if (OP(next) != BRANCH)                /* No choice. */
                    next = OPERAND(scan);		   /* Avoid recursion. */
                else {
                    do {
                        save = reginput;
                        if (regmatch(OPERAND(scan)))
                            return(1);
                        reginput = save;
                        scan = regnext(scan);
                    } while (scan != NULL && OP(scan) == BRANCH);
                    return(0);
                    /* NOTREACHED */
                }
            }
            break;
        case STAR:
        case PLUS: {
                register char nextch;
                register int no;
                register char *save;
                register int min;

                /*
                * Lookahead to avoid useless match attempts
                * when we know what character comes next.
                */
                nextch = '\0';
                if (OP(next) == EXACTLY)
                    nextch = *OPERAND(next);
                min = (OP(scan) == STAR) ? 0 : 1;
                save = reginput;
                no = regrepeat(OPERAND(scan));
                while (no >= min) {
                    /* If it could work, try it. */
                    if (nextch == '\0' || *reginput == nextch)
                        if (regmatch(next))
                            return(1);
                    /* Couldn't or didn't -- back up. */
                    no--;
                    reginput = save + no;
                }
                return(0);
            }
            break;
        case END:
            return(1);        /* Success! */
            break;
        default:
            regerror("memory corruption");
            return(0);
            break;
        }

        scan = next;
    }

    /*
    * We get here only if there's trouble -- normally "case END" is
    * the terminating point.
    */
    regerror("corrupted pointers");
    return(0);
}

/*
- regrepeat - repeatedly match something simple, report how many
*/
static int
regrepeat(p)
char *p;
{
    register int count = 0;
    register char *scan;
    register char *opnd;

    scan = reginput;
    opnd = OPERAND(p);
    switch (OP(p)) {
    case ANY:
        count = strlen(scan);
        scan += count;
        break;
    case EXACTLY:
        while (*opnd == *scan) {
            count++;
            scan++;
        }
        break;
    case ANYOF:
        while (*scan != '\0' && strchr(opnd, *scan) != NULL) {
            count++;
            scan++;
        }
        break;
    case ANYBUT:
        while (*scan != '\0' && strchr(opnd, *scan) == NULL) {
            count++;
            scan++;
        }
        break;
    default:                /* Oh dear.  Called inappropriately. */
        regerror("internal foulup");
        count = 0;        /* Best compromise. */
        break;
    }
    reginput = scan;

    return(count);
}

/*
- regnext - dig the "next" pointer out of a node
*/
static char *
regnext(p)
register char *p;
{
    register int offset;

    if (p == &regdummy)
        return(NULL);

    offset = NEXT(p);
    if (offset == 0)
        return(NULL);

    if (OP(p) == BACK)
        return(p-offset);
    else
        return(p+offset);
}

#ifdef DEBUG

STATIC char *regprop();

/*
- regdump - dump a regexp onto stdout in vaguely comprehensible form
*/
void
regdump(r)
regexp *r;
{
    register char *s;
    register char op = EXACTLY;        /* Arbitrary non-END op. */
    register char *next;
    extern char *strchr();


    s = r->program + 1;
    while (op != END) {        /* While that wasn't END last time... */
        op = OP(s);
        printf("%2d%s", s-r->program, regprop(s));        /* Where, what. */
        next = regnext(s);
        if (next == NULL)                /* Next ptr. */
            printf("(0)");
        else
            printf("(%d)", (s-r->program)+(next-s));
        s += 3;
        if (op == ANYOF || op == ANYBUT || op == EXACTLY) {
            /* Literal string, where present. */
            while (*s != '\0') {
                putchar(*s);
                s++;
            }
            s++;
        }
        putchar('\n');
    }

    /* Header fields of interest. */
    if (r->regstart != '\0')
        printf("start `%c' ", r->regstart);
    if (r->reganch)
        printf("anchored ");
    if (r->regmust != NULL)
        printf("must have \"%s\"", r->regmust);
    printf("\n");
}

/*
- regprop - printable representation of opcode
*/
static char *
regprop(op)
char *op;
{
    register char *p;
    static char buf[50];

    (void) strcpy(buf, ":");

    switch (OP(op)) {
    case BOL:
        p = "BOL";
        break;
    case EOL:
        p = "EOL";
        break;
    case ANY:
        p = "ANY";
        break;
    case ANYOF:
        p = "ANYOF";
        break;
    case ANYBUT:
        p = "ANYBUT";
        break;
    case BRANCH:
        p = "BRANCH";
        break;
    case EXACTLY:
        p = "EXACTLY";
        break;
    case NOTHING:
        p = "NOTHING";
        break;
    case BACK:
        p = "BACK";
        break;
    case END:
        p = "END";
        break;
    case OPEN+1:
    case OPEN+2:
    case OPEN+3:
    case OPEN+4:
    case OPEN+5:
    case OPEN+6:
    case OPEN+7:
    case OPEN+8:
    case OPEN+9:
        sprintf(buf+strlen(buf), "OPEN%d", OP(op)-OPEN);
        p = NULL;
        break;
    case CLOSE+1:
    case CLOSE+2:
    case CLOSE+3:
    case CLOSE+4:
    case CLOSE+5:
    case CLOSE+6:
    case CLOSE+7:
    case CLOSE+8:
    case CLOSE+9:
        sprintf(buf+strlen(buf), "CLOSE%d", OP(op)-CLOSE);
        p = NULL;
        break;
    case STAR:
        p = "STAR";
        break;
    case PLUS:
        p = "PLUS";
        break;
    default:
        regerror("corrupted opcode");
        break;
    }
    if (p != NULL)
        (void) strcat(buf, p);
    return(buf);
}
#endif

#define STRCSPN
/*
* The following is provided for those people who do not have strcspn() in
* their C libraries.  They should get off their butts and do something
* about it; at least one public-domain implementation of those (highly
* useful) string routines has been published on Usenet.
*/
#ifdef STRCSPN
/*
* strcspn - find length of initial segment of s1 consisting entirely
* of characters not from s2
*/

static int
strcspn(s1, s2)
char *s1;
char *s2;
{
    register char *scan1;
    register char *scan2;
    register int count;

    count = 0;
    for (scan1 = s1; *scan1 != '\0'; scan1++) {
        for (scan2 = s2; *scan2 != '\0';)        /* ++ moved down. */
            if (*scan1 == *scan2++)
                return(count);
        count++;
    }
    return(count);
}
#endif


#ifndef CHARBITS
#define UCHARAT(p)        ((int)*(unsigned char *)(p))
#else
#define UCHARAT(p)        ((int)*(p)&CHARBITS)
#endif

/*
- regsub - perform substitutions after a regexp match
*/
void
regsub(prog, source, dest)
regexp *prog;
char *source;
char *dest;
{
    register char *src;
    register char *dst;
    register char c;
    register int no;
    register int len;
    extern char *strncpy();

    if (prog == NULL || source == NULL || dest == NULL) {
        regerror("NULL parm to regsub");
        return;
    }
    if (UCHARAT(prog->program) != MAGIC) {
        regerror("damaged regexp fed to regsub");
        return;
    }

    src = source;
    dst = dest;
    while ((c = *src++) != '\0') {
        if (c == '&')
            no = 0;
        else if (c == '\\' && '0' <= *src && *src <= '9')
            no = *src++ - '0';
        else
            no = -1;

        if (no < 0) {        /* Ordinary character. */
            if (c == '\\' && (*src == '\\' || *src == '&'))
                c = *src++;
            *dst++ = c; }
        else if (prog->startp[no] != NULL && prog->endp[no] != NULL) {
            len = prog->endp[no] - prog->startp[no];
            (void) strncpy(dst, prog->startp[no], len);
            (void) strncpy(prog->var[no], prog->startp[no], len);
            CG_Printf("number %i var %s \n", no, prog->var[no] );
            dst += len;
            if (len != 0 && *(dst-1) == '\0') {/* strncpy hit NUL. */
                regerror("damaged match string");
                return;
            }
        }
    }
    *dst++ = '\0';

}


